A typical communications network comprises a plurality of nodes or subscriber stations. Illustratively, such networks are arranged so that any given subscriber station can communicate selectively and exclusively with any other subscriber station or with a group of other subscriber stations.
As more advanced communications services such as enhanced video and interactive data communications become available, greater bandwidth is needed. Such bandwidth may be provided by implementing the network using optical technology including single mode optical fibers. In one type of optical network, a plurality of subscriber stations may be interconnected by means of a central hub switch. Each of the subscriber stations s connected to the hub switch by means of a bidirectional optical fiber link. However, in conventional optical fiber networks the hub switch itself is an electronic switch. Accordingly, information received by the hub switch from one of the subscriber stations must first undergo optical-to-electronic conversion. The converted electrical information is then electronically processed by the hub switch and converted back to optical form for transmission out of the hub switch to another of the subscriber stations.
One problem with this type of arrangement is that such electronic processing is limited in speed. A typical electronic gate can process information at a rate of up to about one gigabit per second. However, this is only a fraction of the bandwidth that can be provided using optical technology.
Accordingly, it is desirable to provide an all optical network which connects a plurality of subscriber stations. The all optical network should be arranged to provide simultaneous and exclusive message paths between subscriber pairs. An example of such an all optical network is disclosed in Cheung-Kobrinski-Loh U.S. patent application Ser. No. 948,244, entitled "Multi-Wavelength Optical Telecommunications System", filed Dec. 31, 1986, and now abandoned and assigned to the assignee hereof. The contents of this application are incorporated herein by reference.
This patent application describes a network in which each subscriber station has a transmitter capable of transmitting radiation at a unique wavelength associated with the particular station. Each station also has a receiver capable of receiving all of the wavelengths produced by the various transmitters in the network. A passive optical hub element is adapted to receive radiation over optical fiber links at a different wavelength from each of the transmitters and transmit over optical fiber links a fraction of the power received at each wavelength to all receivers. Thus, each subscriber station receives a fraction of the power transmitted by every other subscriber station. The receiver at each station is tunable to a given one of the wavelengths transmitted thereto so that communication between pairs of stations in the network can be achieved.
Another optical telecommunications network is disclosed in Chung-Kerner-O'Connor-Salehi-Wei U.S. patent application Ser. No. 923,332, entitled "Encoding and Decoding for Code Division Multiple Access Communication Systems", filed on Oct. 27, 1986 and now U.S. Pat. No. 4,779,266 issued Oct. 18, 1988 and assigned to the assignee hereof. The contents of this patent application are incorporated herein by reference. This patent application describes an optical network in which an optical pulse is transmitted to a selected one out of a plurality of potential receiving stations by coding the pulse in a manner so that it is detectable by the selected receiving station but not the other receiving stations. Such coding is accomplished by dividing each pulse into a plurality of intervals known as "chips". Each chip may take on the value logic "1" indicated by relatively large radiation intensity or the value logic "0" indicated by a relatively small radiation intensity. The chips comprising each pulse are coded with a particular pattern of logic "1"'s and logic "0"'s characteristic of the receiving station or stations to which it is to be transmitted. Each receiving station is provided with optical receiving equipment capable of regenerating an optical pulse when it receives a pattern of chips coded in accordance with its own unique sequence but cannot regenerate the pulse if the pulse is coded with a different sequence or code. A detailed discussion of the mathematical properties of the codes used in this network is provided in the patent application.
It is an object of the present invention to provide an alternative optical telecommunications system capable of supporting multiple simultaneous connections between subscriber pairs. In particular, mode locked lasers are capable of producing ultra-short pulses in which the phases of all of the Fourier components are coherently rather than randomly related. As shown below, phase coding of the Fourier components which comprise such optical pulses provide the basis of an inventive optical network in which one subscriber station can communicate selectively and exclusively with one or more other subscriber stations.